<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <button>点击发送ajax请求</button>
  <body>
    <script>
      let btn = document.querySelector("button");
      btn.onclick = function () {
        let xhr = new XMLHttpRequest();
        xhr.open("post", "/postData");
        xhr.setRequestHeader("content-type", "application/json");
        xhr.send(JSON.stringify({ type: 0 }));
        xhr.onload = function (res) {
            if (xhr.status >= 200 && xhr.status < 300) {
            console.log(xhr.responseText);
          }
         
        };
      };
    </script>
  </body>
</html>
